With the development of digital technology in recent years, playback methods using recording media such as optical disks and magnetic disks have been put to practical use for playback of digitized sources, and various kinds of data compression/multiplexing methods have been proposed. MPEG (Moving Picture Experts Group) is one of these methods, and especially MPEG1 is used for video CD. In MPEG1, I pictures are included in GOP (group of pictures), and each I picture maintains its independence by itself, differently from B pictures (Bidirectionally predictive coded pictures) and P pictures (Predictive coded pictures). By continuously decoding the I pictures (hereinafter referred to as I playback), a trick play such as fast forward playback (i.e., forward I playback) or fast reverse playback (i.e., backward I playback) is achieved.
However, since no navigation information is included in a video CD while it is included in a DVD (Digital Versatile Disc), the position of GOP which appears in a bit stream cannot be predicted. Therefore, in an AV decoding/playback apparatus such as a video CD player, in order to perform I playback, a bit stream is divided into unit lengths without considering GOP included in the bit stream, the thus obtained bit streams are sequentially input to the AV decoder for decoding, and I pictures included in each bit stream are sequentially displayed.
More specifically, in the conventional I playback, a bit stream is divided into plural bit streams having the same bit length, and these divided bit streams are sequentially read from the disk and input to the AV decoder for decoding. Every time an I picture appears, the I picture is displayed. When decoding of one divided bit stream is completed, the following divided bit stream is input to the AV decoder.
In the conventional I playback, however, the time required for moving the playback point (seek point) on the bit stream in the I playback by one divided bit length is equal to the time required for reading and decoding one divided bit stream and, therefore, the time for moving the playback point on the bit stream for fast-forward playback or fast-reverse playback is increased. As a result, high-speed forward playback or reverse playback cannot be achieved.
The present invention is made to solve the above-described problems and has for its object to provide an AV decoder control method and an AV decoder control apparatus which can perform high-speed I playback using an AV decoder.